In this article we describe the characteristics of a large integrated linear optical device containing Mach-Zehnder interferometers and describe its potential use as a physically unclonable function. We propose that any tunable interferometric device of practical scale will be intrinsically unclonable and will possess an inherent randomness that can be useful for many practical applications. The device under test has the additional use-case as a general-purpose photonic manipulation tool, with various applications based on the experimental results of our prototype. Once our tunable interferometric device is set to work as a physically unclonable function, we find that there are approximately 6.85x10E35 challenge-response pairs, where each challenge can be quickly reconfigured by tuning the interferometer array for subsequent challenges.